with \(\odot \)  being the Khatri-Rao product; see, e.g, [1]}. That is, the dependency is still bilinear, but any entry of \(\widehat{\mathbf {y}}\)  depends on all the bilinear terms \([\mathbf {h}]_\text{l}[\mathbf {x}]_n\) . Interestingly, while in the time domain \(\Psi =\mathbf {U}\) , in GSP the matrices representing the graph Fourier transform (GFT) for filters and signals are in general not the same.
